[Kat-A-Tonic]

I find I have to drop 1 or 2 gears to pass quickly.

Which is a common complaint , even among a lot of SS bikes . That means you want more torque , in which case "no replacement for displacement " .

Amen to that. 8)

[The CyberPoet]

I find I have to drop 1 or 2 gears to pass quickly.

Which is a common complaint , even among a lot of SS bikes . That means you want more torque , in which case "no replacement for displacement " .

+1 in general. There is a direct relationship, at least among ambient-air breathing engines, between displacement and actual max torque delivered. The GSXR600 in the example above doesn't deliver any significantly larger amount of torque than the kat (within a few percentage points) -- it just can deliver it more often per minute because of the higher redline..

Special sidenote: you can effectively replace displacement by cramming the same amount of fuel-air mixture used by a larger engine (at a much higher compression ratio, using a supercharger or turbocharger for forced induction) into a smaller engine to get similar power benefits. But the motor now has to put up with much larger stresses (in every technical engineering sense, from stresses to heat). Moving to a larger displacement, only lightly stressed engine is a far better solution for long term happiness if you're simply seeking more torque on demand.

Cheers,
=-= The CyberPoet

[BLACKDEATH]

um cyber. if you were going to turbo or supercharge a bike you would want to drop compression not go up in compression. That is why turbo pistons are low comp pistons. im sure you allready know that. but im sure some others dont.

[Mazda Bob]

Switch to the V Twin or 4 lineup

[The CyberPoet]

um cyber. if you were going to turbo or supercharge a bike you would want to drop compression not go up in compression. That is why turbo pistons are low comp pistons. im sure you allready know that. but im sure some others dont.

To clarify it to the newbs, you physically alter the compression chamber size, usually by shimming the gaskets and/or using replacement pistons that increase the volume remaining in the detonation chamber, to reduce the ambient compression ratio (the compression ratio without figuring in the turbo's or supercharger's boost input). You do this, because once the boost pressure from the turbo or supercharger is elevated enough, you run the risk (if you hadn't modified) that the compression ratio in the cylinder would exceed the realistic limit on what you can compress gasoline-air mixtures to without sponateous pressure-based detonation (for high-RPM engines with cylinders in the 150 - 200cc range, 13.5:1 on premium, 16:1 or so on specialty race fuels), and you also face mechanical risks of engine components self-destructing in mere moments..

This is not to say that in actual operation, the mixture in the cylinder won't be running under significantly higher total pressure than the stock (non-force-induced) engine would be. Or to try to clarify it with a tad bit of math and a bit of over-simplification:
If the stock 149cc cylinder runs 11.7:1 compression, then the engine compresses 14.7 psi ambient to 11.7 times that amount, or about 180 psi [idealized; due to leakage at the valves & rings, usually 150-165 psi actual], at peak torque RPM, before detonating it. Footnote 1.
If you bolt on a forced induction system that provides say 8 lbs of boost at that same peak torque (RPM), you've changed the equation from compressing 14.7 psi by 11.7 times to compressing 22.7 psi by 11.7 times, resulting in about 266 psi [idealized] before detonation. This is a figure is too high for most motorcycle engine parts & blocks, and far too much for most fuels to handle reasonably well. So by increasing the detonation chamber size (but retaining the same bore & stroke length), you drop the 11.7 compression factor downwards to reduce the total pressure excerted Footnote 2.


Footnotes:
1 - yes, I know I simplified the process by pretending detonation happens at Top Dead Center (TDC) instead of 4 to 11 degrees Before Top Dead Center (BTDC). I'm trying to make it clear to those not in the know without clouding up the issue with more details.
2 - in the car world, it's not uncommon to use a diesel block & engine components for a serious turbo upgrade, because while gasoline engines are designed to handle 130 - 200 psi in the chamber, diesels run on significantly higher ratios and their engines are designed to handle pressures in the 280 - 350 psi range readily (some as high as 600 psi for some turbo-diesel designs), allowing you to design boost pressures that are pretty astronomical. Unfortunately, unlike a chevy 350 block (which you can easily find in a diesel variant), there aren't any mass-produced-for-public-use diesel motorcycle engines readily available. One of the reasons Turbo Diesel (direct) Injected [TDi] engines run so efficiently is because of this difference in compression levels exploiting the maximum power available in the space used. In theory, if you could build a direct-injection motorcycle engine capable of handling diesel-like compression levels, you could make a super-high compression ratio gasoline motorcycle engine that worked and it would literally blow the doors off everything else road-worthy on the planet.

KNOW THIS:
according to an article in the newest issue of BIKE [UK] many turbo'd/supercharged motorcycles use too small a turbo/supercharger, basing the turbo or supercharger size primarily on the engine displacement (incorrectly). Sizing the turbo/supercharger should factor in the total volume of air that moves through the engine over time -- in other words, a 1 liter 4-cylinder motorcycle engine running at 14k RPM will consume 7000 liters of air a minute without boosting (about the amount a typical 2.6 - 2.8 liter car engine would running 5k RPM).

Cheers,
=-= The CyberPoet

[Mojoe]

I find I have to drop 1 or 2 gears to pass quickly.

Which is a common complaint , even among a lot of SS bikes . That means you want more torque , in which case "no replacement for displacement " .

Amen to that. 8)

that's why I went 1100 many many years ago, and could never consider going smaller. I can pass pretty quickly without down shifting in many cases.
if I drop 2 gears, it's probably because i am passing like 4, 5, or more vehicles at once

[kwebbel]

I find I have to drop 1 or 2 gears to pass quickly.

Which is a common complaint , even among a lot of SS bikes . That means you want more torque , in which case "no replacement for displacement " .

What are you talking about? I do only ride in 5th nowadays, don't bother to shift anymore 8)

[The CyberPoet]

Sounds like someone wants an automatic FJR...


Cheers,
=-= The CyberPoet

[kwebbel]

FJR? Yammie? I must confess I did consider it while looking for a new touringbike. compared to the Beemer the Yammie lost on every aspect (as all Nippons did) but the price.
Beemers are expensive but believe me Marc they are superior to any ricer...

[StevieB]

CP- You Rock!!!
That is an awsome answer...

Yes, it is an good answer- as far as it goes. It addresses the QUANTATIVE (i.e. technical) side of the question, but does nothing to address the QUALATIVE side. How are they both like to ride? What do they each do well, middling, and poorly? What are the relative merits of owning or riding one, vs. owning or riding the other?

I could sit here and specuate, but the truth is, I am not very qualified to answer those qualatative questions- I have never ridden or owned a gixxer. I could answer if the question was along the lines of "Bandit vs. Kat," as I have owned both at the same time, and made it a point to ride them back-to-back. So, IMHO, what we need here is someone who DOES or HAS owned them both, and can make an informed comparison.

After THAT has been done, THEN you can blast the questioner.

[The CyberPoet]

:P


=-= The CyberPoet

[BLACKDEATH]

Cyber. i figured you knew. I should have expected a good writeup on it. And that was a good writeup on it.

[md86]

I find I have to drop 1 or 2 gears to pass quickly.

Which is a common complaint , even among a lot of SS bikes . That means you want more torque , in which case "no replacement for displacement " .

Special sidenote: using a supercharger or turbocharger

Ah turbo , yeah , that helps with a smaller engine . But , you still gotta wait for the turbo to spool up , whereas the bigger engine has the torque on tap RIGHT NOW . Supercharger skips that hassle , but parasitic losses on top end ...... PLUS , it's a LOT more work . I'd LOVE something with a supercharger just for the cool factor , but alas , I'm poor .

[Macodad]

so... being painfully mechanically incompetent and new to this, am I understanding that a 600kat and 600 gsxr are pretty close in comparison regarding available torque?
I don't really want/need speed/top end, where (on the street) am I gonna need to go +160km ?
I just would like more reaction when I roll on the throttle in 5th or 6th.
Suggestions on mods to get this? (sorry to steal the thread)

[The CyberPoet]

so... being painfully mechanically incompetent and new to this, am I understanding that a 600kat and 600 gsxr are pretty close in comparison regarding available torque?

Yup, they both produce almost identical torque... the gsxr can just produce it more often as it gets up into the higher RPM's that the Kat can't reach.

I don't really want/need speed/top end, where (on the street) am I gonna need to go +160km ?
I just would like more reaction when I roll on the throttle in 5th or 6th.
Suggestions on mods to get this? (sorry to steal the thread)

Sprocketing changes (gearing advantages) will get you more acceleration at any speed, but cut your top speed and consume more fuel (because you'll be running higher RPM's at any given speed).
More details, pro's & con's, here:

http://www.motorcycleanchor.com/katana/Katana_sprockets.html

Cheers,
=-= The CyberPoet